dye

dye,

any substance, natural or synthetic, used to color various materials, especially textiles, leather, and food. Natural dyes are so called because they are obtained from plants (e.g., alizarinalizarin, or 1,2-dihydroxyanthraquinone, mordant vegetable dye obtained originally from the root of the madder plant (Rubia tinctorum), in which it occurs as a glucoside. The term also includes a group of synthetic dyestuffs prepared from coal-tar derivatives......Click the link for more information., catechucatechuor cutch,extract from the heartwood of Acacia catechu, a leguminous tree of the pulse family, native to India and Myanmar. Catechu is a fast brown dye used for various shades of brown and olive, including the familiar khaki, and also in tanning......Click the link for more information., indigoindigo[Span.; from Lat.,=Indian], important blue dyestuff used in printing inks and for vat dyeing of cotton (see dye). It was anciently produced in India and was known in Egypt, probably c.1600 B.C......Click the link for more information., and logwood), from animals (e.g., cochinealcochineal, natural dye obtained from an extract of the bodies of the females of the cochineal bug (Dactylopius confusus) found on certain species of cactus, especially Nopalea coccinellifera, native to Mexico and Central America......Click the link for more information., kermes, and Tyrian purple), and from certain naturally occurring minerals (e.g., ocherocher, mixture of varying proportions of iron oxide and clay, used as a pigment. It occurs naturally as yellow ocher (yellow or yellow-brown in color), the iron oxide being limonite, or as red ocher, the iron oxide being hematite......Click the link for more information. and Prussian bluePrussian blue,pigment widely used for laundry bluing, in dyeing compounds, and in the manufacture of inks and paints. Several varieties are known, one of which consists of the chemical compound ferric ferrocyanide......Click the link for more information.). They have been almost entirely replaced in modern dyeing by synthetic dyes. Most of these have been prepared from coal tar or petroleum, being formed from an aromatic hydrocarbonhydrocarbon, any organic compound composed solely of the elements hydrogen and carbon. The hydrocarbons differ both in the total number of carbon and hydrogen atoms in their molecules and in the proportion of hydrogen to carbon......Click the link for more information. such as benzene, from which indigo is derived (see also anilineaniline, C6H5NH2, colorless, oily, basic liquid organic compound; chemically, a primary aromatic amine whose molecule is formed by replacing one hydrogen atom of a benzene molecule with an amino group......Click the link for more information.), or anthracene, which yields alizarin.

Although some materials, e.g., silk and wool, can be colored simply by being dipped in the dye (the dyes so used are consequently called direct dyes), others, including cotton, commonly require the use of a mordantmordant[Fr.,=biting], substance used in dyeing to fix certain dyes (mordant dyes) in cloth. Either the mordant (if it is colloidal) or a colloid produced by the mordant adheres to the fiber, attracting and fixing the colloidal mordant dye (see colloid); the insoluble, colored.....Click the link for more information. (see also lakelake,in dyeing, an insoluble pigment formed by the reaction between an organic dye and a mordant. The color of a lake depends upon the mordant as well as the dye used. Generally, lakes are not as colorfast as many inorganic dyes, but their colors are more brilliant......Click the link for more information.). Alizarin is a mordant dye and the color it gives depends upon the mordant used. Dyes are classified also as acidic or basic according to the medium required in the dyeing process. A vat dye, e.g., indigo, is so called from the method of its application; it is first treated chemically so that it becomes soluble and is then used for coloring materials bathed in a vat.

When the materials become impregnated with the dye, they are removed and dried in air, the indigo reverting to its original, insoluble form. The process by which a dye becomes "attached" to the material it colors is not definitely known. One theory holds that a chemical reaction takes place between the dye and the treated fiber; another proposes that the dye is absorbed by the fiber.

Dyeing is an ancient industry. The Chinese, Persians, and Indians used natural dyes many centuries ago, including indigo, probably the oldest dye in use, and Tyrian purple, derived from a species of snail. The Egyptians prepared some brilliant colors. In the 13th and 14th cent. dyeing assumed importance in Italy; the methods employed were carried to other parts of Europe and, as new dyes became known, the dyeing industry flourished and grew. Cochineal was introduced from Mexico. Finally, in the 19th cent. the work of W. H. PerkinPerkin, Sir William Henry,1838–1907, English chemist. In 1856 he discovered the first aniline dye (aniline purple, known as mauve and mauveine); by founding a factory to make it, Perkin established the aniline dye industry in England. He was knighted in 1906......Click the link for more information. and Adolf von BaeyerBaeyer, Adolf von(Johann Friedrich Wilhelm Adolf von Baeyer) , 1835–1917, German chemist. He taught at Berlin and Strasbourg and in 1875 succeeded Liebig at Munich......Click the link for more information. produced the first synthetic dyes.

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